The symptoms of premenstrual syndrome (PMS) consist of mood, cognitive, and behavioral disturbances occurring in the premenstrual phase of the menstrual cycle. They may become severe enough to cause suicidal depression or psychosis. Objective physiologic parameters that correlate with the subjective symptoms of PMS need to be identified in order to delineate this syndrome further and possibly to suggest better forms of treatment. First, this study examined sleep, temperature and activity changes across the menstrual cycle in women with moderate to severe premenstrual syndrome and in normal volunteers. Two months of baseline activity recording, objective ratings and self-ratings of sleep, mood, and energy were obtained. Subjects were then admitted to the hospital where they underwent sleep EEG and temperature recordings two nights a week for the duration of one menstrual cycle. Premenstrual syndrome may represent a variant of affective disorder. Therefore, treatment modalities found to be effective in the major affective disorders may be useful in treating patients with PMS. For example, sleep deprivation which induces transient remissions in affective disorder may do the same in PMS. Furthermore, sleep deprivation lowers prolactin, and hyperprolactinemia has been associated with mood disturbances in patients with PMS. Therefore, the effects of sleep deprivation were investigated in these patients. Prolonged intense light exposure alleviates symptoms in patients with seasonal affective disorder. Since symptoms of SAD and PMS are similar, prolonged intense light exposure or treatment with the beta blocking drug, atenolol, which, like bright light, suppresses melatonin was evaluted as a possible treatment for PMS. Results of sleep deprivation and light treatment experiments may increase our understanding of the pathophysiological mechanisms of PMS and the relationship between PMS and affective disorders.